Can lid and manufacturing method therefor

ABSTRACT

By conducting a strict study on a plate thickness, a pressure resistance is improved while satisfying the demand for further reduction of the plate thickness. 
     A can lid has a center panel part, a panel wall part, a chuck wall radius part, a chuck wall part, and a curl part. t 2 &gt;t 1  holds, where t 1  represents a plate thickness of the center panel part, and t 2  represents a plate thickness of a bottom end of the panel wall part.

TECHNICAL FIELD

The present invention relates to a can lid and a manufacturing method therefor.

BACKGROUND ART

A metal can for filling a beverage or the like therein hermetically encloses contents by seaming a can lid to an opening end of a bottomed cylindrical can barrel in a case of a two-piece can. For such a can lid, the one with a stay-on tab type opening tab has been generally adopted. The can lid is seamed to the opening end of the can barrel after filling contents in the can barrel. For this reason, generally, the can lid is supplied to a filling destination in a stacked state separately from the can barrel.

The can lid has a center panel part to which an opening tab is mounted, and has, on a surrounding side thereof, an annular groove part into which an outer edge projection of an inner tool (seaming chuck) of a seamer is inserted. Further, the can lid has a curl part to be seamed to the opening end of the can barrel at an outer circumference of the annular groove part (see, for example, PTL 1 described below).

Then, for a structure of such a can lid, a panel wall part is shaped as a wall part in a groove at the annular groove part, a chuck wall radius part is shaped at a portion extending from the wall part in the groove to an wall part outside the groove at the annular groove part, and a chuck wall part is shaped at a portion extending from the wall part outside the groove to the curl part.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Patent Application Publication No. 2019-112143 -   [PTL 2] Japanese Patent Application Publication No. H03-275443

SUMMARY OF INVENTION Technical Problem

A metal can has been demanded to be reduced in plate thickness as much as possible in order to save material resources and reduce a weight thereof. However, when the plate thickness is reduced, strength (pressure resistance) matters in a case where the pressure in the can increases.

For the can lid, when the pressure in the can increases, a force of pushing up the center panel part upward acts thereon. For this reason, when the pressure in the can increases abnormally, the annular groove part reversely projects upward, resulting in that the annular groove part and the center panel part may be in a state projecting upward in an angular shape, i.e., so-called buckling may be caused. Particularly, when the content is a carbonated drink, or the like, upon an abnormal increase in temperature in the can due to ambient environment or the like, buckling becomes more likely to be caused.

To address this, for the structure of the can lid for increasing the pressure resistance, various countermeasures have been studied in, for instance, conventional art shown in the PTL 1. However, with the countermeasures, as the foregoing conventional art, the importance has been placed only on the shape design, e.g., a first curve part and a second curve part are provided at the chuck wall part; and the relationship between a radius of curvature of the first curve part and a radius of curvature of the second curve part is regulated. No strict study on the plate thickness has been conducted.

The present invention has been proposed in order to address such a problem. It is an object of the present invention to provide a can lid with a high pressure resistance while meeting a demand for a smaller plate thickness on the basis of a stricter study on the plate thickness, or the like.

Solution to Problem

In order to solve such a problem, a can lid in accordance with the present invention includes the following configuration.

A can lid having a center panel part, a panel wall part, a chuck wall radius part, a chuck wall part, and a curl part, characterized in that t2>t1 holds, where t1 represents a plate thickness of the center panel part, and t2 represents a plate thickness of a bottom end of the panel wall part.

Advantageous Effects of Invention

A can lid having such a feature can provide the can lid with a high pressure resistance while meeting a demand of more reducing a plate thickness, and can attain an improvement of the pressure resistance at the can lid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view showing a partial cross section of a can lid.

FIG. 2 is an explanatory view showing a manufacturing process of a can lid.

FIG. 3 is an explanatory view showing a shape body in the manufacturing process (FIG. 3 at (a) is a shape body shaped by step S1 to step S3, FIG. 3 at (b) and (c) each is a shape body shaped by step S4, and FIG. 3 at (d) is a can lid finally obtainable).

FIG. 4 is an explanatory view showing a blank stamping step (FIG. 4 at (a) is before stamping, and FIG. 4 at (b) is after stamping).

FIG. 5 is an explanatory view of an outer circumferential part drawing step (FIG. 5 at (a) is during drawing, and FIG. 5 at (b) is drawing completed).

FIG. 6 is an explanatory view of a panel part drawing step (FIG. 6 at (a) is at the time of start of drawing, and FIG. 6 at (b) is at the time of completion of drawing).

FIG. 7 is an explanatory view of a panel part pressing down step (FIG. 7 at (a) is at the time of start of pressing down, and FIG. 7 at (b) is during pressing down).

FIG. 8 is an explanatory view of a panel part pressing down step (FIG. 8 at (a) is pressing down completed, and FIG. 8 at (b) is shaped product extraction).

FIG. 9 is an explanatory view showing an example of addition of ironing at the panel part drawing step.

FIG. 10 is an explanatory view showing an example of another shape of an embodiment of the present invention.

FIG. 11 is a view showing the measurement position of a plate thickness of the middle part of the chuck wall part (FIG. 11 at (a) is a view showing the measurement position of another embodiment of FIG. 10 , and FIG. 11 at (b) is a view showing the measurement position of an embodiment.

DESCRIPTION OF EMBODIMENTS

Below, embodiments of the present invention will be described by reference to the accompanying drawings. In the following description, the same reference numerals and signs in different drawings show the sites having the same function, and an overlapping description in respective drawings will be appropriately omitted.

As shown in FIG. 1 , a can lid 1 in accordance with an embodiment of the present invention has a center panel part 1A, a panel wall part 1B, a chuck wall radius part 1C, a chuck wall part 1D, and a curl part 1E. The center panel part 1A is a generally flat portion of a central portion of the can lid 1, and is provided with a score or an opening tab in a case of a stay-on type.

At an outer edge of the center panel part 1A, there is a curve portion r1. A portion extending downward linearly from a terminal of the curve portion r1 is the panel wall part 1B. Then, a portion which is a curve portion r2 to be shaped under the panel wall part 1B, and includes the bottom of an annular groove part Cs to be shaped at an outer circumference of the center panel part 1A is the chuck wall radius part 1C. Further, a linear or partially curved potion extending upward from an outer upper end of the chuck wall radius part 1C, a portion from an outer wall of the annular groove part Cs further to a front of a curve of the curl part 1E, is the chuck wall part 1D.

Then, in the can lid 1 in accordance with an embodiment of the present invention, t2>t1 holds, where t1 represents a plate thickness of the center panel part 1A, and t2 represents a plate thickness of a bottom end of the panel wall part 1B. The plate thickness t1 of the center panel part 1A is a value close to an original plate thickness of a material to be processed before shape processing of the can lid 1.

The bottom end of the panel wall part 1B is a boundary portion between the chuck wall radius part 1C and the curve portion r2. For the can lid 1, by adopting a novel method for shape processing of the chuck wall radius part 1C, the plate thickness t2 of the bottom end of the panel wall part 1B is made larger than the plate thickness t1. This enables the can lid 1 with a still higher pressure resistance in addition to a conventional shape design. By making the plate thickness t2 larger than 1.01 times the plate thickness t1 (t2>1.01*t1), it is possible to obtain a can lid 1 with a still higher pressure resistance.

Further, for the can lid 1, by making a plate thickness t3, where t3 represents a plate thickness of the chuck wall radius part 1C, larger than the plate thickness t1, and preferably making the plate thickness t3 larger than 1.01 times the plate thickness t1>1.01*t1), it is possible to obtain a can lid 1 with a high pressure resistance.

Further, for the can lid 1, t1>t4 holds, where t4 represents a plate thickness of a middle part of the chuck wall part 1D, namely, a plate thickness at a position one half a substantial height of the can lid as shown in FIG. 1 . Accordingly, by making the middle part of the chuck wall part 1D thin, relatively less affected by a pressure resistance, it is possible to reduce a weight of the can lid 1 while keeping a prescribed pressure resistance.

For the can lid 1, by partially increasing the plate thicknesses of the panel wall part 1B and the chuck wall radius part 1C of the annular groove part Cs to be shaped at the outer circumference of the center panel part 1A, it is possible to further increase a pressure resistance in addition to the rationalization of the conventional shape design of the annular groove part Cs and the portion extending therefrom to the curl part 1E.

For the can lid 1, the plate thicknesses of the panel wall part 1B and the chuck wall radius part 1C of the annular groove part Cs to be shaped at the outer circumference of the center panel part 1A can be made larger than the original plate thickness of the material to be processed (the plate thickness t1 of the center panel part 1A). For this reason, it becomes possible to reduce the original plate thickness of the material to be processed as much as possible, so that saving of material resources and weight reduction can be effectively implemented.

Below, a manufacturing method of the can lid 1 will be described. The manufacturing process of the can lid 1 has a blank stamping step S1, an outer circumferential part drawing step S2, a panel part drawing step S3, and a panel part pressing down step S4 as shown in FIG. 2 .

In the steps, a shape body M1 shown in FIG. 3 at (a) is shaped by the step S1 to the step S3, and in the step S4, the shape body M1 is subjected to press down processing of a panel part p (a processed part to be processed into the center panel part 1A). As a result, shape bodies M2 and M3 shown in FIG. 3 at (b) and (c) are shaped, finally resulting in the can lid 1 shown in FIG. 3 at (d).

Each step will be specifically described below. In each step, an upper tool U and a lower tool L shown in FIGS. 4 to 8 are used as process tools. The upper tool U includes an inner tool U1 and an outer tool U2. The lower tool L includes a fixed inner tool L1, a movable inner tool L2, a movable outer tool L3, and a fixed outer tool L4.

In the blank stamping step S1, as shown in FIG. 4 at (a), a material to be processed M is inserted into between the upper tool U and the lower tool L. As shown in FIG. 4 at (b), stamping by a processing surface a of the outer tool U2 and a processing surface b of the fixed outer tool L4 due to descent of the upper tool U shapes a shape body M01 in a disk shape.

At the outer circumferential part drawing step S2, further, the upper tool U descends. As a result, as shown in FIG. 5 at (a), a lower surface c of the outer tool U2 and an upper surface d of the movable outer tool L3 sandwich an outer circumferential part of a shape body M02. Thus, the outer circumferential part of the shape body M02 is subjected to drawing processing by a processing surface e of the movable inner tool L2. Further, descent of the upper tool U causes the lower surface c of the outer tool U2 to press down the movable outer tool L3, so that a drawing processing on a shape body M03 progresses by a processing surface f of the outer tool U2 and a processing surface g of the movable inner tool L2 as shown in FIG. 5 at (b).

At the panel part drawing step S3, as shown in FIG. 6 at (a), the upper tool U descends further. As a result, a processing surface h of the outer tool U2 and the processing surface e of the movable inner tool L2 sandwich an outer circumferential part of a shape body M04. Thus, a panel part p of the shape body M04 touches an upper surface of the fixed inner tool L1. Accordingly, drawing processing of the panel part p is performed. Then, in this state, as shown in FIG. 6 at (b), the upper tool U descends further, so that with an outer circumferential part of a shape body M05 being sandwiched, the movable inner tool L2 is pressed down. Simultaneously, a lower surface of the inner tool U1 and the upper surface of the fixed inner tool L1 sandwich the panel part p. Accordingly, drawing processing of the panel part p progresses.

Then, at the panel part pressing down step S4, as shown in FIG. 7 at (a), with an outer circumferential part of a shape body M06 being sandwiched between the processing surface e and the processing surface h, the movable inner tool L2 presses up the outer tool U2. As a result, as shown in FIG. 7 at (b), the panel part p of the shape body M06 is relatively pressed down with respect to the outer circumferential part, so that a shape body M07 is shaped.

Then, as shown in FIG. 8 at (a), relative pressing down of the panel part p is further progressed. As a result, a processed part to be processed into the chuck wall radius part 1C between the panel part p and an outer circumferential part of a shape body M08 is forced into a groove part j provided between the fixed inner tool U2 and the movable inner tool L2. As a result of this, the panel warm part 1B and the chuck wall radius part 1C are shaped. Further, due to the relative pressing down of the panel part p, the curl part 1E is shaped into an outer circumferential part sandwiched between the processing surface e and the processing surface h. Furthermore, the center panel part 1A is shaped in the panel part p sandwiched between the lower surface of the inner tool U1 and the upper surface of the fixed inner tool L1. Subsequently, as shown in FIG. 8 at (b), the upper tool U and the lower tool L are disengaged, and a shaped product of the can lid 1 is taken out.

Subsequently, although not shown, the outermost circumferential part of the shaped product of the can lid 1 is curled into a shape suitable for seaming by a known method, and a sealing compound is applied to an inner surface portion thereof. Further, according to the intended purpose, the panel part is subjected to a step such as rivet processing, score processing, or caulking of a tab, resulting in completion of a can lid.

With the manufacturing process, the panel wall part 1B and the chuck wall radius part 1C are shaped by pressing down the panel part p which is the processed part to be processed into the center panel part 1A and the processed part to be processed into the chuck wall radius part 1C is forced into the groove part j. For this reason, a shape process is accomplished without direct touch between the processing surface of the process tool and the panel wall part 1B and the chuck wall radius part 1C. Further, pressing down of the panel part p causes the processed parts to be processed into the panel wall part 1B and the chuck wall radius part 1C to be applied with a compression stress in a direction orthogonal to a plate thickness direction. Accordingly, such plastic deformation as to result in an increase in plate thickness is performed.

Further, as a process tool, as shown in FIG. 9 , a die obtained by providing a fixed inner tool L10 with an ironing convex part k1 is used. Then, the shape body is ironed between an inner processing surface k2 of the outer tool U2 of the upper tool U and the ironing convex part k1. As a result, at the panel part drawing step S3, ironing can be added to the middle part of the chuck wall part 1D. Thus, when ironing is added to a part (particularly, a central part) of the chuck wall part 1D, a plate thickness of a part of the chuck wall part 1D can be reduced. As a result of this, it is possible to effectively enhance the pressure resistance of the can lid 1 while satisfying a demand for saving material resources and reduction of the weight.

Incidentally, the manufacturing process is a method for performing from blank stamping to the shaped product of the can lid 1 by one stroke in upper and lower dies. However, the series of steps can also be performed in a plurality of stages using different dies. Particularly, an action of the compression stress in the direction orthogonal to the plate thickness direction due to pressing down of the panel part p in the panel part pressing down step S4 is maximized in a state depicted in FIG. 8 at (a), namely, in a state in which the processed part is forced into the bottom of the groove part j. For this reason, a following control becomes possible: panel pressing down is divided into a plurality of stages; and at each stage, the panel pressing down is performed with the die including the groove bottom; as a result, the region to be increased in plate thickness is allowed to be wider.

Examples

Using a coil coat material obtained by coating an Al alloy (A5182-H19) with a plate thickness of 0.26 mm with an outer surface paint in an amount of 15 mg/dm² and an inner surface paint in an amount of 100 mg/dm² as a to-be-processed material M, the can lid 1 was shaped with the manufacturing process. Thus, a plate thickness of each part was measured. The example is shown in Table 1 below. Incidentally, t5 is a plate thickness of the upper end of the panel wall part 1B. Herein, shaping was performed in the same manner as in Example 1, except that the middle part of the chuck wall part 1D was subjected to ironing at an ironing ratio of about 7% with an outer diameter of the fixed inner tool L1 Φh=51.58 mm for Example 1, Φh=52.18 mm for Example 2, and Φh=51.58 mm for Example 3.

TABLE 1 Plate Pressure thickness resistance site t1 t2 t3 t4 t5 (MPa) Example 1 0.260 0.290 0.271 0.275 0.280 0.752 Example 2 0.260 0.302 0.279 0.285 0.291 0.766 Example 3 0.260 0.307 0.282 0.256 0.301 0.777 Comparative 0.260 0.242 — 0.258 0.240 0.691 Example

As shown in Table 1, in Example 1, the plate thickness t2 is larger than 1.01 times the plate thickness t1. In Example 2, the plate thickness t2 and the plate thickness t3 are larger than 1.01 times the plate thickness t1. Further, in Example 3, the plate thickness t4 is reduced by ironing, so that the metal portion of the processed part to be processed into the panel wall 1B and the chuck wall radius part 1C can be allocated as that much. As a result, the action of the compression stress in the direction orthogonal to the plate thickness direction due to pressing down of the panel part p can further increase the plate thicknesses t2 and t3. Such adjustment of the plate thickness could increase the pressure resistance as compared with Comparative Example accomplished by the conventional method in PTL 2.

As described up to this point, for the can lid 1 in accordance with the embodiment of the present invention, it is possible to obtain the can lid 1 with a high pressure resistance while satisfying a demand for more reducing the plate thickness, and it becomes possible to improve the pressure resistance in the can lid 1. Canned goods obtained by seaming the can lid 1 to the can barrel can reduce a weight of a metal can relative to a content weight while ensuring the high pressure resistance.

Up to this point, the embodiments of the present invention were described by reference to the accompanying drawings. However, the specific configuration is not limited to the embodiments, and even changes or the like of the design within the scope not departing from the gist of the present invention are included in the present invention. Further, the respective embodiments can be combined by applying mutual technologies unless there are particularly inconsistencies and problems. For example, to the can lid 1 having the cross sectional shape as in FIG. 10 described in PTL 1, the combination of the present invention can be applied.

FIG. 11 is a view showing the measurement position of the plate thickness of the middle part of the chuck wall part, where FIG. 11 at (a) is a view showing the measurement position of another embodiment of FIG. 10 , and FIG. 11 at (b) is a view showing the measurement position of an embodiment.

In either case of FIG. 11 at (a) and (b), for the can lid 1, t1>t4 holds, where t4 represents the plate thickness of the middle part of the chuck wall part 1D, namely, the plate thickness at the position at a height one half the substantial height of the can lid. Also in another embodiment, by making thin the middle part of the chuck wall part 1D relatively less affected by the pressure resistance, it is possible to reduce the weight of the can lid 1 while keeping a prescribed pressure resistance.

Incidentally, the other embodiment of FIG. 11 at (a) and the embodiment of FIG. 11 at (b) show partial cross sections after seaming the portion of the can lid 1 of FIG. 10 and the portion of the can lid 1 of FIG. 1 to their can barrels, respectively. Even the comparison between state of FIGS. 10 and 1 before seaming and states of FIG. 11 after seaming does not indicate a change in substantial height between before and after seaming of the can lid 1. Accordingly, the plate thicknesses t4 of the other embodiment FIG. 11 at (a) and the embodiment FIG. 11 at (b) are roughly at the same position.

REFERENCE SIGNS LIST

-   1 Can lid -   1A Center panel part -   1B Panel wall part -   1C Chuck wall radius part -   1D Chuck wall part -   1E Curl part -   U Upper tool -   L Lower tool -   p Panel part 

1. A can lid having a center panel part, a panel wall part, a chuck wall radius part, a chuck wall part, and a curl part, wherein t2>t1 holds, where t1 represents a plate thickness of the center panel part, and t2 represents a plate thickness of a bottom end of the panel wall part.
 2. The can lid according to claim 1, wherein t2>1.01*t1 holds, where t1 represents a plate thickness of the center panel part, and t2 represents a plate thickness of a bottom end of the panel wall part.
 3. The can lid according to claim 1, wherein t3>1.01*t1 holds, where t3 represents a plate thickness of the chuck wall radius part.
 4. The can lid according to claim 1, wherein t1>t4 holds, where t4 represents a plate thickness of a middle part of the chuck wall part.
 5. Canned goods using the can lid according to claim
 1. 6. A manufacturing method for the can lid according to claim 1, wherein the chuck wall radius part is shaped by relatively pressing down a processed part to be processed into the center panel part.
 7. The manufacturing method for the can lid according to claim 6, wherein ironing is added to a part of the chuck wall part. 